Electrochemical cell and process for splitting a sulfate solution and producing a hyroxide solution sulfuric acid and a halogen gas

Abstract

The present invention relates to an electrochemical cell and a process for producing a hydroxide solution, sulfuric acid and a halogen gas from a hydrogen halide and a sulfate solution. In particular, the sulfate solution may be an alkali metal sulfate solution, such as sodium or potassium sulfate solution, an alkaline earth metal sulfate solution or an ammonium sulfate solution. The cell and the process may use either an anhydrous or an aqueous hydrogen halide, namely, hydrogen chloride, hydrogen fluoride, hydrogen bromide and hydrogen iodide, to a respective dry halogen gas, such as chlorine, fluorine, bromine, or iodine, to produce hydrogen ions in order to split the alkali metal solution and form the sulfuric acid. The cell has two membrane-electrode assemblies, where an anode is disposed in contact with one membrane, and a cathode is disposed in contact with another membrane. The sulfate solution is fed in between the membrane-electrode assemblies.

What is claimed is: 
     
       1. A process for producing a hydroxide solution, sulfuric acid and a halogen gas from a hydrogen halide and a sulfate solution, wherein: (a) a sulfate solution is fed to a first compartment of an electrochemical cell, wherein the sulfate solution comprises sulfate ions and cations;   (b) hydrogen halide is fed to a second compartment of the electrochemical cell and is transported to an anode of the cell;   (c) the hydrogen halide is oxidized at the anode to produce halogen gas and protons, and the protons are transported through a first cation-transporting membrane;   (d) the first membrane rejects the sulfate ions and the sulfate ions join the protons to form a sulfuric acid solution;   (e) water is fed to a third compartment of the cell and is reduced at a cathode of the cell to hydrogen and hydroxyl ions; and   (f) a second membrane rejects the hydroxyl ions and the hydroxyl ions are joined with the cations to form a solution of hydroxide.   
     
     
       2. The process of claim 1, wherein the hydroxide solution is an alkali metal hydroxide solution, the sulfate solution is an alkali metal sulfate solution, and the cation is an alkali metal ion. 
     
     
       3. The process of claim 2, wherein the alkali metal is sodium. 
     
     
       4. The process of claim 2, wherein the alkali metal is potassium. 
     
     
       5. The process of claim 1, wherein the hydroxide solution is an alkaline earth metal hydroxide solution, the sulfate solution is an alkaline earth metal sulfate solution, and the cation is an alkaline earth metal ion. 
     
     
       6. The process of claim 5, wherein the alkaline earth metal is magnesium. 
     
     
       7. The process of claim 5, wherein the alkaline earth metal is calcium. 
     
     
       8. The process of claim 1, wherein the hydroxide solution is an ammmonium hydroxide solution, the sulfate solution is an ammonium hydroxide sulfate solution, and the cation is an ammonium ion. 
     
     
       9. The process of claim 1, wherein the hydrogen halide is selected from the group consisting of hydrogen chloride, hydrogen fluoride, hydrogen bromide and hydrogen iodide. 
     
     
       10. The process of claim 9, wherein the halogen gas is selected from the group consisting of chlorine gas, fluorine gas, bromine gas and iodine gas. 
     
     
       11. The process of claim 1, wherein molecules of essentially anhydrous hydrogen halide are fed to the second compartment and are oxidized at the anode. 
     
     
       12. The process of claim 1, wherein ions of aqueous hydrogen halide are fed to the second compartment and are oxidized at the anode. 
     
     
       13. A process for producing a sodium hydroxide solution, sulfuric acid and chlorine from essentially anhydrous hydrogen chloride and a sodium sulfate solution, wherein: (a) a sodium sulfate solution is fed to a first compartment of an electrochemical cell, wherein the sodium sulfate solution comprises sulfate ions and sodium ions;   (b) molecules of essentially anhydrous hydrogen chloride are fed to a second compartment of the electrochemical cell and are transported to an anode of the cell;   (c) the molecules of anhydrous hydrogen chloride are oxidized at the anode to produce halogen gas and protons, and the protons are transported through a first cation-transporting membrane;   (d) the first membrane rejects the sulfate ions and the sulfate ions join the protons to form a sulfuric acid solution;   (e) water is fed to a third compartment of the electrochemical cell and is reduced to hydrogen and hydroxyl ions; and   (f) a second membrane rejects the hydroxyl ions and the hydroxyl ions are joined with the sodium ions to form a solution of hydroxide.   
     
     
       14. An electrochemical cell for producing a hydroxide solution, sulfuric acid and a halogen gas from a hydrogen halide and a sulfate solution, comprising: (a) means for introducing a sulfate solution to a first compartment of the cell, wherein the sulfate solution comprises sulfate ions and cations;   (b) means for introducing hydrogen halide to a second compartment;   (c) means for oxidizing the hydrogen halide to produce halogen gas and protons;   (d) first cation-transporting means for transporting the protons therethrough, wherein the first cation-transporting means is disposed in contact with the oxidizing means, the first cation-transporting means rejects the sulfate ions, and the sulfate ions join the protons to form a sulfuric acid solution;   (e) means for introducing water to a third compartment;   (f) means for reducing the water to hydrogen and hydroxyl ions; and   (g) second cation-transporting means for rejecting the hydroxyl ions and for transporting the cations therethrough, wherein the second cation-transporting means is disposed in contact with the reducing means and the hydroxyl ions are joined with the cations to form a solution of hydroxide.   
     
     
       15. The electrochemical cell of claim 14, wherein the oxidizing means comprises means for oxidizing molecules of essentially anhydrous hydrogen halide to produce essentially dry halogen gas. 
     
     
       16. The electrochemical cell of claim 14, wherein the oxidizing means comprises means for oxidizing ions of aqueous hydrogen halide to produce wet halogen gas. 
     
     
       17. The electrochemical cell of claim 14, wherein the first cation-transporting means comprises a first membrane, the second cation-transporting means comprises a second membrane, and the first and second membranes face each other. 
     
     
       18. The electrochemical cell of claim 14, wherein the oxidizing means is an anode and the reducing means is a cathode, further comprising an anode mass flow field disposed in contact with the anode, and a cathode mass flow field disposed in contact with the cathode. 
     
     
       19. The electrochemical cell of claim 18, wherein the anode and the cathode mass flow fields have flow channels formed therein, and the flow channels of the anode mass flow field and the flow channels of the cathode mass flow field are parallel to each other. 
     
     
       20. The electrochemical cell of claim 19, wherein the flow channels of the anode mass flow field and of the cathode mass flow field are both vertical. 
     
     
       21. The electrochemical cell of claim 19, wherein each of the anode and the cathode comprise an electrochemically active material. 
     
     
       22. The electrochemical cell of claim 21, wherein the anode and the cathode are gas diffusion electrodes. 
     
     
       23. The electrochemical cell of claim 22, wherein the catalyst loading of the electrochemically active material is in the range of 0.10 to 0.50 mg/cm 2 . 
     
     
       24. The electrochemical cell of claim 21, wherein the electrochemically active material comprises one of the following: platinum, ruthenium, osmium, rhenium, rhodium, iridium, palladium, gold, titanium and zirconium, and the oxides, alloys and mixtures thereof. 
     
     
       25. The electrochemical cell of claim 24, wherein the electrochemically active material is applied as a film from ink onto the membrane. 
     
     
       26. The electrochemical cell of claim 25, whereon the loading of the electrochemically active material is at least about 0.017 mg/cm 2 . 
     
     
       27. The electrochemical cell of claim 24, wherein the first and the second cation-transporting means each comprises a copolymer of tetrafluoroethylene and poly-sulfonyl fluoride vinyl ether-containing pendant sulfonic acid groups. 
     
     
       28. The electrochemical cell of claim 27, wherein the electrochemically active material of the anode is ruthenium oxide. 
     
     
       29. The electrochemical cell of claim 28, wherein the electrochemically active material of the anode is platinum. 
     
     
       30. The electrochemical cell of claim 21, wherein the electrochemically active material is bonded to a support structure. 
     
     
       31. The electrochemical cell of claim 30, wherein the support structure comprises carbon paper. 
     
     
       32. The electrochemical cell of claim 30, wherein the support structure comprises graphite cloth. 
     
     
       33. The electrochemical cell of claim 30, wherein the electrochemically active material comprises a catalyst material on a support material. 
     
     
       34. The electrochemical cell of claim 33, wherein the support material comprises particles of carbon and particles of polytetrafluoroethylene. 
     
     
       35. The electrochemical cell of claim 34, wherein the electrochemically active material is bonded by the particles of polytetrafluoroethylene to the support structure.